The present disclosure relates to improvements to the Modigliani process as generally described in U.S. Pat. Nos. 2,081,060; 2,546,230; and 2,913,037. Subsequent improvements and variations of the Modigliani process have been made and are known in the art. Little has been done to improve upon the efficiency of the manufacturing methods and apparatus either through new control methods or through process changes.
The Modigliani process and its progeny generally involve a melting furnace feeding molten glass which discharges fine glass filaments. The glass fibers are in turn wrapped around a rotating drum. During the deposition of the fibers on the rotating drum, resins are applied to the surface of the glass as it is accumulated on the rotating drum.
Strands of molten glass exit the melting furnace through a multi-orifice metallic plate (bushing plate) attached to the underside of the melting furnace. The diameter of strands is determined by a combination of the diameters of orifices disposed within the bushing plate, surface velocity of the rotating drum positioned below the melting furnace, onto which glass filaments are pulled and accumulated, and chemical composition of the glass.
Drum length is a determinant of the length of the cured fiberglass media that emerges from the fiberglass curing apparatus. Customers of cured fiberglass generally desire lightweight fiberglass in roll lengths that are up to 1200 feet. These customers also desire heavier weight rolls in lengths as short as 200 feet.
Loft height of the cured fiberglass is an important characteristic. Customers generally desire lofts from ¼ inch to 6 inches. Thinner lofts compress more easily when rolled while thicker lofts are more difficult to compress. The reason for this is that the cross linked resin bonds in cured fiberglass resist bending. The bending resistance increases with the distance the cross linked bond must travel when the loft is compressed in the process. If the bond is subjected to too much deformation, it ultimately breaks, which lessens the ability of the cured fiberglass to return to its specified loft when the roll is unwound.
There is an interaction between drum circumference and curing apparatus width which affects the geometry of filament cross linking in the finished product. The design of the curing apparatus is constrained by many factors, one of which is the width of the upper loft-setting conveyor belt (or chain) which is used to set the loft of the product. Because customer product specifications for loft have narrow tolerances, typically + or −one eighth of an inch or one quarter of an inch, there can be very little deflection of the upper loft-setting conveyor across its width. At design widths exceeding 132 inches, it becomes mechanically complex and prohibitively expensive to limit deflection sufficiently. If the width of the unexpanded fiberglass mat—which is generally equal to the circumference of the drum—is greater than 22 feet, it becomes very difficult to cure the filaments such that the cross linked filaments are cured at angles of approximately 90 degrees. Such curing produces longitudinal and transverse stiffness of the finished media that are approximately equal (which is a common customer requirement.)
Longitudinal filament adherence introduces defects in stiffness and rigidity in either the X or Y (horizontal) axes. It also diminishes compressive strength and reduces the ability of media, especially in air filtration applications, to capture and hold solid and liquid particulates.
If the circumference of the rotating drum (and thus the approximate unexpanded mat width) is less than 12 feet or greater than 22 feet, the filaments will adhere to each other longitudinally for excessive distances in either the X or Y axes as they are cured, which will create insufficient finished product stiffness in one of those two axes. Such conditions also produce insufficient compressive strength (another typical customer requirement) in the loft of the finished product. In air filtration applications, those conditions can diminish the ability of the media to capture and hold particulates. Insufficient compressive strength furthermore leads to cosmetic defects such as bunching of filaments, thereby lessening the product's appeal to customers, both in air filtration and light filtration applications.
Spinning drums ranging from 12 feet to 24 feet in length with circumferences ranging from 12 to 22 feet have varying drum weights along with a variety of typical rotational speeds. The combination of drum length and drum circumferences with varying rotational speed creates vibrations, which tend to result in premature failure of a drum shaft. Failure to properly calculate the appropriate shaft diameters required for safe operation of rotatable drums of various dimensions at various surface velocities has led to shaft failures which creates unsafe conditions.
Several resin binder formulations are known in the art and may be sprayed onto the glass fiber. Generally, the process is designed such that the swath of filaments is sprayed with binder almost immediately after deposition on the drum. The resin thoroughly coats the most recently applied glass filaments and causes the glass filaments to adhere to rest of the filament mat. Proper binder coverage of the filaments may not be achieved if the centrifugal force of the rotating drum overcomes the viscosity of the binder and forces binder closer to the drum to migrate toward the filaments further from the drum.
There remains a considerable need for systems, apparatuses and methods that can improve the efficiency and quality of the manufacture of continuous glass filament media.